all you really want to do when turtleling is well build units that you need to defend with when i start to turtle i usually start with lets say a shit ton of repair guys and a few rockets(thy act as aa and if you start getting artyed you put them into second mode and you've got a shield that will defend against that arty fire)always have a few in norm mode for AA reasons add a few heavy tanks that can take a beating and your done when defending a bridge always have a arty with you constantly pouring shells on the bridge for safety reasons and well theres my short little tutorial oh and if there's a turret near you position repair it and get it up and running and i think that's it........... if i forgot something leave it in the comments......... radar would help spot targets for arty so bring one of them to the spot your camping at and well ill end it here